There are fewer of the disk-shaped creatures, and the ones that remain are getting punier, according to Georgia Southern University researcher Sophie George.

Beachcombers may be playing a role in the creature's decline, she said. Her message to beachgoers as the summer tourist season heats up: Only collect dead sand dollars, identified by their cream-colored shells.

On Sunday, with Tybee packed for the holiday weekend, she quickly spotted three sand dollars drying on a pair of surf shoes at the water's edge.

Picking up the largest, she noted an abnormal tint to its surface. The animal was exuding a green, blood-like substance.

"He's stressed," George said.

Sand dollars reproduce in the summer and come closer to shore to do so. It's a double-whammy that makes them easier to collect just when it hurts their population most.

"Around this time (of year) they're moving inshore," George said. "Around this time we should be finding a lot of them. But over the years we've found their numbers decreasing."

Over the last decade, Tybee sand dollars appear to have gotten less abundant and smaller than sand dollars at nearby islands such as Wassaw, said George, an associate professor of biology at GSU.

Size matters because big sand dollars are the best reproducers. Unfortunately, they're also most prized by collectors.

George noted another sign of distress in the Tybee population when she began counting sand dollars' eggs.

"Egg size is good indication what's going on in invertebrates," George said. "When things are going well they tend to produce lots of small eggs. When things get bad, the size of the egg starts to increase."

George doesn't have enough data to be certain of the trend, but it doesn't look good. Eggs produced on Tybee were larger than those on Wassaw or Jekyll islands.

George, originally from the West African nation of Sierra Leone, got her doctorate at the University of Paris studying sea urchins, a relative of the sand dollar. She came to the United States for postdoctoral studies. After George began work at Georgia Southern, in 1995, she switched her focus to the sand dollar because sea urchins were too hard to find here.

She and her students have encountered beachgoers who didn't know the sand dollars they were collecting were alive.

One day in 1998 they discovered what seemed like sand dollar carnage. "There was a mound of sand dollars that was abandoned," she said. "That was hundreds. We estimated that 10,000 were removed (from Tybee) one summer."

She doubts anybody could find that many sand dollars to heap into a pile at Tybee now.

"I try to nicely ask if they know those are live animals," she said. "People look at me like they're shooting darts with their eyes and say 'Yes, I do.'"

When they're alive, sand dollars are brownish on top and purple underneath. Their hair-like spines wiggle on the underside, Bartoo said.

Sand dollars sometimes die off en masse for unknown reasons, George said. She saw the phenomenon on Wassaw once when hundreds of sand dollars covered the beach.

"I don't know what killed them, she said. "It could be (heat) stress, pollution. The very next time I went things seemed to be going well for them."

Mass mortality only seems to occur in the summer, another reason it's best for hot-weather beachgoers to leave sand dollars alone.

"When people collect it they make it worse," she said. "There's the natural factor plus our own human effects."

Sand dollars aren't just beautiful, George said, they're also industrious. Like thousands of tiny underwater Roombas they're constantly vacuuming the sand. "They have to keep the sand clean, basically," George said. "In their absence the beaches could look really messy. They rework the sediments by cleaning it. They also control the abundance of other little species that live in the sediment. If you remove them you can throw off an entire ecosystem."

The three sand dollars George found drying in the sun got a second chance.

Calvin Wilson, the tourist from Tallahassee who had collected them, threw them back in the surf.

George would have liked to have seen them returned to deeper water where they wouldn't be stepped on or re-captured by another tourist, but it was a happier ending than it seemed just minutes before.

People need to be educated that sand dollars are living creatures, she said.

"If it doesn't have eyes and fur you give it less value, but it does have value to the entire beach community."

Sand dollar facts

Sand dollars are marine animals related to starfish and sea urchins. The most common species along the Georgia coast is Mellita isometra.

Where do they live? On the sandy sea floor in both Atlantic and Pacific oceans.

What do they look like? Dark brownish-gray disks with a flattened external skeleton or exoskeleton. Small spines that look like fine hair cover the shell and allow the animal to burrow under the sand. On the upper half of the sand dollar's body, spines also serve as gills.

What do they eat? They clean up the sand, eating microscopic algae. Sand dollars use their fuzzy spines, aided by tiny hairs, to ferry food particles along their bodies to their mouth in the center of their underside.

Did you know?

In quiet waters, sand dollars stand on end like slices of bread in a loaf. Several hundred can pack into one square yard.

The sand dollar's jaw has five teethlike sections to grind up tiny plants and animals. Sometimes a sand dollar "chews" its food for fifteen minutes before swallowing. It can take two days for the food to digest.

Scientists can age a sand dollar by counting the growth rings on the plates of the exoskeleton. Sand dollars usually live six to 10 years.